Lowestoft and Great Yarmouth regional Astronomers based in Lowestoft and Kessingland Astronomy group which is part of Lyra based in Kessingland

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Monday, 20 May 2013

SPA ENB No. 353

The SOCIETY for POPULAR ASTRONOMY

Electronic News Bulletin No. 353 2013 May 19

Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is Britain's liveliest astronomical society, with members all over the world. We accept subscription payments online at our secure site and can take credit and debit cards. You can join or renew via a secure server or just see how much we have to offer by visiting http://www.popastro.com/

POSSIBLE FRAGMENTS FROM 1908 TUNGUSKA METEOR EXPLOSION Universe Today

The 1908 explosion over the Tunguska region in Siberia has always been an enigma. The leading theories of what caused the high-altitude explosion are that an asteroid or comet shattered in an airburst event, but no reliable trace of such a body has ever been found. A newly published paper, however, refers to three different potential meteorite fragments found in the sand bars in a body of water in the area, the Khushmo River. The fragments have all the hallmarks of being meteorites from the event, but there is an oddity inasmuch as the researcher actually found the fragments 15 years ago but has only recently published his findings. Like the recent Chelyabinsk air-burst event, the Tunguska event probably produced a shower of fragments from the exploding parent body. The explosion flattened trees over a radius of 25 km. Luckily that region was largely uninhabited; only one person was said to have been killed, and there were very few people who reported the explosion. Forensic-like research has suggested that the blast was 1,000 times more powerful than the Hiroshima bomb explosion, and it created an earthquake that registered 5 on the Richter scale.

Previous expeditions to the region did not find any meteorites, though one expedition in 1939 by Russian mineralogist Leonid Kulik found a piece of melted glassy rock containing bubbles, which was considered evidence of an impact event. But the sample was somehow lost and is not available for a modern analysis. In 1998 Andrei Zlobin from the Russian Academy of Sciences made several drill holes in the peat bogs in the area, and while he found evidence of the explosion, he did not at first find any meteorites. He gathered from a river shoal about 100 samples of rocks that had features of potential meteorites, but further examination reduced the number to just three rocks with tell-tale features like melting and regmaglypts (impressions on the surfaces of meteorites, caused by ablation as the hot rock tears through the atmosphere at high speed). Zlobin claims that after the expedition he investigated thermal processes and mathematical modelling of the Tunguska impact; he used tree-ring evidence to estimate the temperatures from the event, and concluded that rocks already on the ground would not have been changed or melted from the blast, and therefore any rocks showing evidence of melting should be from the impactor itself. Zlobin says that he has not yet carried out a detailed chemical analysis of the rocks, to determine their chemical and isotopic composition. But he does say that the stony fragments do not rule out a comet, since the nucleus could easily contain rock fragments. There is nothing actually definitive from Zlobin's new paper, and there is the question of why he waited so long to conduct his study, but his work does offer some hope for a fuller explanation of the Tunguska event than has yet been obtained. Clearly there is more work to be done, particularly the chemical analysis, perhaps with international cooperation and corroboration.

EARTH AND MOON HAVE COMMON WATER SOURCE Brown University

New research finds that water inside the Moon's mantle came from primitive meteorites, the same source as is thought to have supplied most of the water on the Earth. The findings raise new questions about the process that formed the Moon. The Moon is thought to have formed from a disc of debris left when another object hit the Earth 4.5 billion years ago, very early in the Earth's history. Scientists have long assumed that the heat from such an impact would cause hydrogen and other volatile elements to boil off into space, meaning that the Moon must have started off completely dry. But recent spacecraft and new research on samples from the Apollo missions have shown that the Moon actually has water, both on its surface and beneath. By showing that water on the Moon and on Earth came from the same source, the new study offers evidence that the Moon's water has been there all along.

The simplest explanation for what the researchers found is that there was water on the proto-Earth at the time of the impact. Some of that water survived the impact, and is what we see in the Moon. To find the origin of the Moon's water, the team looked at melt inclusions found in samples brought back from the Apollo missions. Melt inclusions are tiny dots of volcanic glass trapped within crystals called olivine. The crystals prevent water escaping during an eruption and enable researchers to get an idea of what the inside of the Moon is like. Research in 2011 found that the melt inclusions have plenty of water -- as much water in fact as lavas forming on the Earth's ocean floor. To find the origin of that water, the team looked at the isotopic composition of the hydrogen trapped in the inclusions. They measured the amount of deuterium in the samples in comparison with the amount of ordinary hydrogen. Water molecules originating from different places in the Solar System have different amounts of deuterium. In general, bodies that formed closer to the Sun have less deuterium than ones formed farther out. They found that the deuterium/hydrogen ratio in the melt inclusions was relatively low and matched the ratio found in carbonaceous chondrites, meteorites originating in the asteroid belt near Jupiter and thought to be among the oldest objects in the Solar System. That means that the source of the water on the Moon is primitive meteorites, not comets as some scientists thought. Comets, like meteorites, are known to carry water and other volatiles, but most comets formed in the far reaches of the Solar System and tend to have high deuterium/hydrogen ratios -- much higher than in the Moon's interior, where the samples in this study are supposed to have come from. The new data provide the best evidence yet that the carbon-bearing chondrites were a common source for the volatiles in the Earth and Moon, and perhaps the entire inner Solar System. Recent research has found that as much as 98% of the water on Earth also comes from primitive meteorites, suggesting a common source for water on Earth and water on Moon. The easiest way to explain that is that the water was already present on the early Earth and was transferred to the Moon. If the Moon was formed by a massive impact with the early Earth, it makes sense that the water in both would share a common source, but there is still a question as to how that water was able to survive such a violent collision.

CASSINI OBSERVES METEOROIDS HITTING SATURN'S RINGS NASA

The Cassini spacecraft has provided the first direct evidence of small meteoroids crashing into Saturn's rings and breaking into streams of rubble. The meteoroids Cassini detected range in size from about a centimetre to several metres. The new results imply that present-day impact rates for small particles at Saturn are about the same as those at the Earth. The Saturnian equinox in 2009 was an especially good time to see the debris left by meteoroid impacts. The edge-on illumination of the rings by the Sun made clouds of debris look bright against the darkened rings. Researchers now think that meteoroids probably break up on a first encounter with the rings, creating smaller, slower pieces that then enter into orbit around Saturn. The impact into the rings of those secondary meteoroids creates clouds of debris. The tiny particles forming the clouds have a range of orbital speeds around Saturn. As a result they are soon are pulled into diagonal, extended bright streaks such as Cassini observed.

HUBBLE FINDS DEAD STARS POLLUTED WITH PLANETARY DEBRIS RAS

The Hubble telescope has found signs of Earth-like planets in an unlikely place -- the atmospheres of two white-dwarf stars. The white dwarfs are small, dim remnants of stars and are about 150 light-years away in the Hyades star cluster, in Taurus. Hubble's spectroscopic observations identified silicon in their atmospheres; silicon is a major ingredient of the rocky material of the Earth and other terrestrial planets in the Solar System. The silicon may have come from asteroids that were shredded by the white dwarfs' very strong gravity when they approached too close to the stars.

FIRST BIOLOGICAL EVIDENCE OF A SUPERNOVA Technische Universitaet Muenchen

In fossil remnants of iron-loving bacteria, researchers have found a radioactive iron isotope that they trace back to a supernova in our cosmic neighbourhood. This is the first possible biological signature of a supernova. The age determination of a deep-drill core from the Pacific Ocean showed that the supernova must have occurred about 2.2 million years ago, roughly around the time when the modern human developed.

Most of the chemical elements have their origins in core-collapse supernovae. When a star ends its life in a gigantic explosion, it throws most of its mass into space. The radioactive iron isotope Fe-60 is produced almost exclusively in such supernovae. Because its half-life of 2.62 million years is short compared to the age of the Solar System, no supernova iron should be present on Earth. Therefore, any discovery of Fe-60 on Earth would indicate a relatively recent supernova in our cosmic neighbourhood. In 2004, Fe-60 was discovered in a ferro-manganese crust obtained from the floor of the equatorial Pacific Ocean. Its geological dating puts the event around 2.2 million years ago. Some support for an event around that time has come from Pacific Ocean sediment brought up as a drill core. So-called magnetotactic bacteria live on the ocean floor. They make within their cells hundreds of tiny crystals of magnetite (Fe3O4), each approximately 80 nanometres in diameter. The bacteria obtain the iron from atmospheric dust that enters the ocean. Astrophysicists conjectured, therefore, that Fe-60 should also occur within those magnetite crystals produced by magnetotactic bacteria extant at the time of the supernova interaction with our planet. The bacterially produced crystals, when found in sediments long after their host bacteria have died, are called 'magnetofossils'. The drill core referred to above showed indications of Fe-60 at about the right date. A second and much larger core has been obtained but not yet analysed.

CLUSTER OF HYDROGEN CLOUDS BETWEEN NEARBY GALAXIES National Radio Astronomy Observatory.

In a dark, starless patch of intergalactic space, astronomers have discovered a cluster of hydrogen clouds strewn between two nearby galaxies, Andromeda (M31) and Triangulum (M33). The researchers speculate that the rarefied clouds -- each about as massive as a dwarf galaxy -- condensed out of a vast and as-yet undetected reservoir of hot, ionized gas, which could have accompanied an otherwise invisible band of dark matter. Astronomers have known for some time that many seemingly empty stretches of the Universe contain vast but diffuse patches of hot, ionized hydrogen. Earlier observations of the area between M31 and M33 suggested the presence of colder, neutral hydrogen, but they could not see any details to determine if it had a definitive structure or represented a new type of cosmic feature. Now, with high-resolution images, they were able to detect discrete concentrations of neutral hydrogen emerging out of what was thought to be a mainly featureless field of gas.

Astronomers are able to observe neutral atomic hydrogen by the characteristic signal it emits at radio wavelengths. Though hydrogen is abundant throughout the cosmos, between galaxies it can be very tenuous, and the faint signal it emits is difficult to detect. But last year the Green Bank Telescope found that there was a lot of hydrogen between M31 and M33. More thorough studies of the region indicated that much of the gas is clumped together into discrete and apparently self-gravitating clouds that apart from their lack of stars would be called dwarf galaxies. It was possible to track the motion of the clouds, which proved to be travelling through space at velocities similar to M31 and M33, suggesting that they are independent entities and not constituent parts of either galaxy.

EINSTEIN WAS RIGHT -- AGAIN ESO

An international team has discovered a double object that consists of a tiny, but unusually massive, neutron star that spins 25 times each second and is observed as a pulsar, orbited every two and a half hours by a white-dwarf star. The unusual pair constitutes a unique laboratory for testing the limits of physical theories. The pulsar, called PSR J0348+0432, is the remains of a supernova explosion. It is twice as massive as the Sun, but just 20 kilometres across. The gravity at its surface is more than 300 billion times stronger than that on the Earth and at its centre any volume the size of a sugar cube has more than a billion tons of matter in it. Einstein's general theory of relativity, which explains gravity as a consequence of the curvature of space-time, has passed every test since it was first published almost a century ago, but the extreme gravity of PSR J0348+0432 offers an opportunity to push tests into new territory.

The team combined Very Large Telescope observations of the white dwarf with very precise timing of the pulsar from radio telescopes. Such a close binary is expected to radiate gravitational waves and lose energy. That causes the orbital period to lengthen very gradually, and the predictions of the change from general relativity and other competing theories are different. The radio observations are so precise that astronomers have already been able to measure a change in the orbital period of 8 microseconds per year, exactly what Einstein's theory predicts.

PLANETS By Alan Clitherow, SPA Planetary Section Director

Saturn remains the dominant planet in the night sky through late May and into June. As the sky darkens on the 27th of May Saturn becomes visible close to due south and at a magnitude of around 0.47 it should be the first "star" visible in this location; it will be at around 27 degrees above the horizon when first visible from the south of the UK and 22 degrees from central Scotland from around 2230UT. At these elevations Saturn is rather low in the sky which does present some problems with observation. Since we are viewing at a slant through our thick atmosphere, it can be badly affected by any turbulence along the line of sight. With that in mind the air can often be very steady shortly after sunset so it is worth making the effort as the rings are well presented at the moment and with a good view of Saturn's northern hemisphere all the way up to and slightly beyond the pole.

When the Voyager 1 probe passed Saturn it imaged a strange hexagonal pattern of clouds surrounding the North Pole. Much clearer images have been made by the Cassini probe, currently orbiting Saturn, and it seems this feature is a stable hollow hexagon of cloud, slowly rotating around the pole and containing a major rotating storm hovering over the pole itself. Each side of this hexagon is some 14,000 Km long and one or two of its 'points' have recently been imaged from Earth by amateurs from areas with good or excellent 'seeing' conditions. As we move into our summer Saturn will sink lower into the south-western sky and if, like me, you are viewing from Scotland, the planet will be affected by the very short summer nights so I recommend you take the chance to view it while you still can.

Another planetary event of interest is the conjunction of Venus, Mercury and Jupiter low in the north-western sky shortly after sunset. Sadly this will not be visible from anywhere other than the extreme south of the UK and even then only fleetingly. If you do live on the south coast and can find a nice high observation site with a clear horizon it would be worth attempting to see this event on the 27th of May. Venus will become visible as a brilliant point of light, at a magnitude of -3.8, at around 2100UT or shortly thereafter sitting just above the horizon. With the Sun some 8 degrees below the horizon, use binoculars to view Venus and, shortly thereafter, you should see Jupiter and then tiny Mercury in the same field of view. For the rest of the UK this event is likely to be lost in the bright summer evening sky being below the horizon by the time semi-darkness arrives.

Venus and Mercury will improve in visibility as we move into June but this is not a good evening apparition for Mercury from the UK. It will be at its greatest separation from the Sun on the 12th of June (28 degrees behind the Sun) but it will not rise far above the horizon and will be hard to observe in the bright skies. Venus too suffers from its low elevation but will be much easier to find as a brilliant point of light low on the north-western horizon; its elevation rising slowly through the month.

Many people across the Midlands and south of England and south Wales saw a bright fireball heading in a westerly direction at about 20:47 UT on the evening of May 8. Many of the witnesses described it as having a short 'tail' and being green in colour.

Some of the news reports the following morning claimed that the fireball was debris from Comet Halley. The claim was presumably based on someone looking up a list of meteor showers and seeing that the Eta Aquarid meteor shower (which is linked to Comet Halley) is active in early May. However, the radiant of that meteor shower does not rise until the early hours of the morning, so Eta Aquarid meteors cannot be seen during the evening hours.

There was no indication that the fireball was related to the re-entry of man-made space debris. It was most likely a (large) member of the background sporadic meteor activity that is active throughout the year. Indeed, most meteors that appear during the year are part of the sporadic background. Major meteor showers, though briefly impressive, provide only a small fraction of the overall total.

Since the fireball appeared at a time of night when the sky was not yet fully dark, not all automated meteor-camera systems were active. However, the cameras of the UK meteor-observation network had some success in capturing images of the fireball. Their initial analysis of its atmospheric trajectory, which suggests that the fireball passed over Dorset and Devon, can be found at http://snipurl.com/271sjpq . Bear in mind, however, their caution that none of the cameras captured the whole path, so there is some uncertainty in the calculated path.

If you saw that fireball, but have not reported your observation, please do so via the SPA's fireball report form :http://snipurl.com/271skj3

ETA AQUARID OUTBURST By Tony Markham, SPA Meteor Section Director

The Eta Aquarids are one of the year's stronger meteor showers but are only well seen from tropical and southern latitudes. Few are usually seen from the UK because the Eta Aquarid radiant only rises late in the night when morning twilight is already encroaching.

Although the above-noted fireball was not related to the Eta Aquarids, it appears that Eta Aquarid activity was unusually high this year. There was some advanced warning that that might happen. A few days before the shower peak, Mikiya Sato published predictions that, during the course of May 6, the Earth would encounter several dust trails ejected by Comet Halley 8-11 centuries ago. Given the age of those filaments it was quite possible that, rather than seeing sharp peaks in activity, observers would see a broad peak of enhanced activity (owing to the dust having spread out). Sato's best estimate was that the peak would be around twice its normal level -- somewhat similar to that seen for enhancements of the Orionid meteor shower (the Earth's autumn encounter with Comet Halley's dust stream) during the years 2006-2010.

The predictions proved accurate. Alex Pratt (in Leeds), who had never previously imaged any Eta Aquarids, has reported that this year he managed to image several of them late in the nights of May 4-5, 5-6 and 6-7. High rates were reported from Canada and the USA. Radio and radar observers also reported higher than usual activity. For the latest visual results, see the IMO activity curve athttp://snipurl.com/271slyp .

Solar activity improved in April, with some good active regions in both hemispheres. No blank discs were reported. MDF figures were up on last month's, but lower than those in early 2001 when the previous Cycle 23 was at its maximum, the current cycle maximum being due now. In early 2001 monthly MDF figures were in the 6, 7 and 8 range. April this year has 4.69.

Activity in the two hemispheres was about equal in terms of active regions, but the NH had the most individual sunspots. The maximum number of ARs happened from the start of the month to the 11th, when 6-7 were seen. That period's highest Relative Sunspot Number, R, was recorded on the 11th, at 115. The end of the month, from the 25th onwards, showed another increase with 6 ARs almost daily, the highest R figure for that period being 122. Faculae were always evident near the limb.

MDF 4.69 R 64.29

H-ALPHA

Prominences were always seen around the disc, varying in shape, size and intensity, the most spectacular being on the 1st. One on the eastern limb spread far and high northwards away from its base, another in the N towering vertically. They were still visible next day. Filaments were visible in each observation, as was plaging to the ARs, but again no flares were seen.

MDF 5.41

The full Report will be on view, with drawings and pictures, on the Solar link from the SPA home page.

Bulletin compiled by Clive Down

(c) 2013 the Society for Popular Astronomy

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Good Clear Skies--Astrocomet--Colin James Watling

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Various Voluntary work-Litter Picking for Parish Council (Daytime) and also a friend of Kessingland Beach (Watchman) --

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Astrocomet

I started in Astronomy in 1997 when the Comet Hale Bopp got me interested in Astronomy and Skywatching, since then I have joined Lyra and have vastly improved my knowledge of this very rewarding science.